Abstract:

A method of making a flexographic printing sleeve forme includes the steps
of forming a sleeve body by providing one or more at least partially
cured uniform layers on a sleeve carrier; forming a relief image on the
sleeve body by imagewise jetting a curable jetting fluid; and optionally
overall post-curing; characterized in that between formation of the
sleeve body and formation of the relief image no polishing or grinding is
performed.

Claims:

1-15. (canceled)

16. A method of making a flexographic printing sleeve forme comprising the
steps of:forming a sleeve body by providing one or more at least
partially cured uniform layers on a sleeve carrier by:supporting the
sleeve carrier in a vertical position coaxial with a coating
axis;providing an annular coating collar, supplying a curable composition
to the annular coating collar and moving the annular coating collar along
the sleeve carrier in a vertical direction coaxial with the coating axis
thereby coating a layer of the curable composition onto a peripheral
surface of the sleeve carrier;providing an irradiation stage and moving
the irradiation stage in synchronism with the annular coating collar
along the sleeve carrier in the vertical direction while irradiating the
coated layer of the curable composition so as to at least partially cure
the layer of the curable composition onto the peripheral surface of the
sleeve carrier; andoptionally repeating the steps of moving the coating
collar and the irradiation stage while irradiating the layer of the
curable composition coated by the coating collar a plurality of times so
as to apply a plurality of the layers of the curable composition onto the
peripheral surface of the sleeve carrier;forming a relief image on the
sleeve body by imagewise jetting a curable jetting fluid; andoptionally
overall post-curing the sleeve body.

17. The method of making a flexographic printing sleeve forme according to
claim 16, wherein the step of forming the relief image includes:imagewise
jetting at least two layers of the curable jetting fluid or another
curable jetting fluid; andperforming a curing step on each jetted layer.

18. The method of making a flexographic printing sleeve forme according to
claim 16, wherein the one or more at least partially cured layers of the
sleeve body have a total thickness of from 0.2 mm to 3.0 mm.

19. The method of making a flexographic printing sleeve forme according to
claim 17, wherein the one or more at least partially cured layers of the
sleeve body have a total thickness of from 0.2 mm to 3.0 mm.

20. The method of making a flexographic printing sleeve forme according to
claim 19, wherein the total thickness is from 0.4 mm to 1.2 mm.

21. The method of making a flexographic printing sleeve forme according to
claim 16, wherein the curable composition used to form the one or more at
least partially cured layers of the sleeve body includes at least one
urethane (meth)acrylate oligomer, at least one (meth)acrylate monomer,
and at least one photo-initiator system.

22. The method of making a flexographic printing sleeve forme according to
claim 21, wherein the curable composition further includes a silicone
acrylate and/or an inhibitor.

23. The method of making a flexographic printing sleeve forme according to
claim 17, wherein the curable composition used to form the one or more at
least partially cured layers of the sleeve body includes at least one
urethane (meth)acrylate oligomer, at least one (meth)acrylate monomer,
and at least one photo-initiator system.

24. The method of making a flexographic printing sleeve forme according to
claim 23, wherein the curable composition further includes a silicone
acrylate and/or an inhibitor.

25. The method of making a flexographic printing sleeve forme according to
claim 16, wherein at least two of the at least partially cured layers of
the sleeve body have a different composition.

26. The method of making a flexographic printing sleeve forme according to
claim 17, wherein at least two of the at least partially cured layers of
the sleeve body have a different composition.

27. The method of making a flexographic printing sleeve forme according
claim 16, wherein the curable jetting fluid includes at least one
monofunctional monomer, at least one polyfunctional monomer or oligomer,
at least one photo-initiator, and optionally a plasticizer.

28. The method of making a flexographic printing sleeve forme according
claim 17, wherein the curable jetting fluid includes at least one
monofunctional monomer, at least one polyfunctional monomer or oligomer,
at least one photo-initiator, and optionally a plasticizer.

29. The method of making a flexographic printing sleeve forme according to
claim 17, wherein the relief image is formed by imagewise jetting at
least two different curable jetting fluids.

30. A method of flexographic printing comprising the steps of:providing a
flexographic printing sleeve forme prepared according to claim
16;mounting the printing sleeve forme on a flexographic printing
press;supplying ink to the mounted printing sleeve forme; andtransferring
the supplied ink onto a substrate.

31. A method of flexographic printing comprising the steps of:providing a
flexographic printing sleeve forme prepared according to claim
17;mounting the printing sleeve forme on a flexographic printing
press;supplying ink to the mounted printing sleeve forme; andtransferring
the supplied ink onto a substrate.

32. A method of flexographic printing comprising the steps of:providing a
flexographic printing sleeve forme prepared according to claim
19;mounting the printing sleeve forme on a flexographic printing
press;supplying ink to the mounted printing sleeve forme; andtransferring
the supplied ink onto a substrate.

33. A method of flexographic printing comprising the steps of:providing a
flexographic printing sleeve forme prepared according to claim
23;mounting the printing sleeve forme on a flexographic printing
press;supplying ink to the mounted printing sleeve forme; andtransferring
the supplied ink onto a substrate.

34. A method of flexographic printing comprising the steps of:providing a
flexographic printing sleeve forme prepared according to claim
24;mounting the printing sleeve forme on a flexographic printing
press;supplying ink to the mounted printing sleeve forme; andtransferring
the supplied ink onto a substrate.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001]This application is a 371 National Stage Application of
PCT/EP2008/061751, filed Sep. 5, 2008. This application claims the
benefit of U.S. Provisional Application No. 60/971,664, filed Sep. 12,
2007, which is incorporated by reference herein in its entirety. In
addition, this application claims the benefit of European Application No.
07115995.8, filed Sep. 10, 2007, which is also incorporated by reference
herein in its entirety.

BACKGROUND OF THE INVENTION

[0002]1. Field of the Invention

[0003]The present invention relates to a method of making a flexographic
printing sleeve forme including the steps of formation of a sleeve body
by providing one or more at least partially cured uniform layers on a
sleeve carrier followed by imagewise formation of a relief image on the
sleeve body by inkjet printing.

[0004]2. Description of the Related Art

[0005]Flexography is today one of the most important processes for
printing and commonly used for high-volume runs. Flexography is employed
for printing on a variety of substrates such as paper, paperboard stock,
corrugated board, films, foils and laminates. Packaging foils and grocery
bags are prominent examples. Coarse surfaces and stretch films can only
be economically printed with flexography, making it indeed very
appropriate for packaging material printing.

[0006]Analogue flexographic printing formes are prepared from printing
forme precursors including a photosensitive layer on a support or
substrate. The photosensitive layer typically includes ethylenically
unsaturated monomers or oligomers, a photo-initiator and an elastomeric
binder. The support preferably is a polymeric foil such as PET or a thin
metallic plate. Imagewise crosslinking of the photosensitive layer by
exposure to ultraviolet and/or visible radiation provides a negative
working printing forme precursor which after development with a suitable
developer (aqueous, solvent or heat development) leaves a printing
relief, which can be used for flexographic printing. Imaging of the
photosensitive layer of the printing forme precursor with ultraviolet
and/or visible radiation is typically carried out through a mask, which
has clear and opaque regions. Crosslinking takes place in the regions of
the photosensitive layer under the clear regions of the mask but does not
occur in the regions of the photosensitive layer under the opaque regions
of the mask. The mask is usually a photographic negative of the desired
printed image. The analogue preparation of flexographic printing formes
has as major disadvantages the time consuming production of a mask and
the poor dimensional stability of the masks with changing environmental
temperatures or humidities, making it sometimes unsatisfactory for high
quality printing and colour registration. Moreover, the use of separate
masks implies consumption of additional consumables and chemistry, with a
negative impact on the economical and ecological aspects of the
production process, which are often more a concern than the additional
time required for making the masks.

[0007]Digital imaging, using laser recording, of flexographic printing
forme precursors, eliminating the necessity of using a separate mask, is
becoming increasingly important in the printing industry. The
flexographic printing forme precursor is made laser sensitive by
providing e.g. a thin, for UV and visual radiation opaque, infrared (IR)
sensitive layer on top of the photopolymerizable layer. Such a
flexographic printing forme precursor is typically called a "digital" or
"direct-to plate" flexographic printing forme precursor. An example of
such a "direct-to-plate" flexographic printing forme precursor is
disclosed in EP-A 1 170 121. The thickness of the IR-ablative layer(s) is
usually just a few μm. The IR-ablative layer is inscribed imagewise
using an IR laser, i.e. the parts the laser beam is incident on are
ablated and removed. The actual printing relief is produced in the
conventional manner: exposure with actinic light (UV, visible) through
the mask, the mask being imagewise opaque to the crosslinking inducing
light, resulting in an imagewise crosslinking of the photopolymerizable
layer, i.e. relief forming layer. Development with an organic solvent,
water or heat removes the photosensitive material from the unexposed
parts of the relief forming layer and the residues of the IR-ablative
layer. Development may be performed using different developing steps or a
single developing step. Since this method still requires a developing
step, the improvement in efficiency for producing flexographic printing
formes is limited.

[0008]In the direct laser engraving technique for the production of
flexographic printing formes, a relief suitable for printing is engraved
directly into a layer suitable for this purpose. By the action of laser
radiation, layer components or their degradation products are removed in
the form of hot gases, vapours, fumes, droplets or small particles and
nonprinting indentations are thus produced. Engraving of rubber printing
cylinders by lasers has been known since the late 60s of the last
century. However, this technique has acquired broader commercial interest
only in recent years with the advent of improved laser systems. The
improvements in the laser systems include better focusing ability of the
laser beam, higher power, multiple laser beam or laser source
combinations and computer controlled beam guidance. Direct laser
engraving has several advantages over the conventional production of
flexographic printing plates. A number of time consuming process steps,
such as the creation of a photographic negative mask or development and
drying of the printing plate, can be dispensed with. Furthermore, the
sidewall shape of the individual relief elements can be individually
designed in the laser engraving technique.

[0009]The methods described above to prepare a flexographic printing forme
are all subtractive methods, i.e. non printing areas are removed during
wet or dry processing or by laser engraving. Inkjet printing provides an
additive method to prepare a flexographic printing forme. For example
EP-A 1 428 666 and EP-A 1 637 322 disclose a method of preparing a
flexographic printing forme wherein a curable fluid is jetted on a
support or substrate having an ink receiving surface. Advantages of such
a method of preparing a flexographic printing forme are the absence of
any processing steps and the consumption of no more material as necessary
to form a suitable relief image (i.e. removal of non printing areas is no
longer required).

[0010]Conventional flexographic printing formes are "flat" plates. There
are however particular applications requiring the use of continuous
cylindrical formes, the latter typically referred to as sleeves. These
sleeves, in particular seamless sleeves, enable continuous printing and
provide improved registration accuracy and shorter change-over-times on
press. Furthermore, such sleeves may be well-suited for mounting on laser
exposure equipment, where it can replace the drum or be mounted on the
drum for exposure by a laser. Continuous printing has applications in the
flexographic printing of continuous designs in wallpaper, decoration,
gift wrapping paper and packaging.

[0011]Sleeves or sleeve bodies are typically made by coating or mold
casting an elastomeric layer onto a polymeric or metallic cylinder, a so
called basic sleeve, raw sleeve or sleeve carrier. To obtain a uniform
surface of the sleeve body, grinding and/or polishing of the sleeve body
is necessary to obtain good printing results.

[0012]In the present application a sleeve body is a sleeve carrier
provided with one or more at least partially cured layers. A sleeve forme
is obtained upon forming a relief image on the sleeve body.

[0013]A disadvantage of an inkjet method for preparing flexographic
printing sleeve formes by jetting the relief image directly onto the
sleeve carrier, may be (i) a poor adhesion of the relief image, possibly
resulting in a poor runlength and (ii) removal of the relief image after
printing, e.g. by mechanical grinding, to reuse the sleeve carrier,
becomes difficult without damaging the substrate. The latter, removal of
the relief image, is especially important when sleeves are used, since
sleeves are expensive.

[0014]Applying both a so-called "elastomeric floor" layer on the sleeve
carrier in a thickness of typically between 100 μm and several
millimeters and the relief parts with an inkjet method, to avoid the two
mentioned disadvantages, would be very time consuming.

[0015]As an alternative to build the "elastomeric floor", a typical
photopolymer sleeve may be used. Such a photopolymer sleeve typically
includes a sleeve carrier and at least one photocurable layer. Typically,
when using "digital" imaging to prepare the printing formes, as described
above, the "elastomeric floor" layer is established by an overall
exposure through the backside of the support while the relief image is
realized by imagewise exposure through a mask layer. In an inkjet method,
one could cure the complete layer of the photopolymer sleeve, followed by
forming the relief image on the completely cured photolayer by inkjet, as
suggested in EP-A 1 637 322. However, since the photolayer of a typical
photopolymer sleeve is intended to form both the "floor" layer and the
relief layer, the "floor" layer realized in this method would be too
thick.

[0016]It would be advantageous to provide sleeve bodies, including one or
more at least partially cured layers, specifically designed to enable a
relief image to be formed on it by an inkjet method.

[0017]To avoid large stocks of different sleeve bodies, and to enable a
high flexibility in choosing the optimum "elastomeric floor" in view of
the relief image to be built upon it by inkjet, a method wherein the
sleeve body is prepared by applying one or more at least partially cured
layers, followed by forming the relief image on it by inkjet, without the
need to polish and/or grind the sleeve body, would be highly
advantageous. Moreover, it would be particularly advantageous if both
providing the sleeve carrier with a dedicated "elastomeric floor" and
forming the relief image by inkjet can be performed close to the press,
to ensure short access times.

[0018]The unpublished EP-A 06 120 823 (filed 18, Sep. 2006) discloses a
coating device, with limited floor space requirements and supporting a
wide range of sleeve carriers, capable of coating a single or a multitude
of uniform layers of direct laser engraveable material, without the need
for a grinding and/or polishing step.

SUMMARY OF THE INVENTION

[0019]Preferred embodiments of the present invention provide a method of
preparing flexographic printing sleeve formes, supporting a wide range of
sleeve carriers, having a short access time, having a high flexibility
with regard to the materials used and which may be performed "next to the
printing press". Another preferred embodiment of the invention achieves
flexographic printing formes having excellent printing properties, e.g.
good adhesion of the relief image to the "elastomeric floor", resulting
in high run lengths.

[0020]The above described preferred embodiments of the present invention
are realized by a method having the specific features as set out below.
Further advantageous embodiments of the invention are also set out below.

[0021]Other elements, features, steps, characteristics and advantages of
the present invention will become more apparent from the following
detailed description of the preferred embodiments with reference to the
attached drawings.

[0024]FIG. 3 shows a cross-sectional view of an embodiment of an annular
irradiation stage.

[0025]FIG. 4 shows a cross-sectional view of another embodiment of an
annular irradiation stage.

[0026]FIG. 5 shows an embodiment of the invention incorporating a spinning
irradiation stage.

[0027]FIG. 6 shows an embodiment of the invention incorporating a spinning
laser beam for irradiating the coated layer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028]The present invention relates to a method of making a flexographic
printing sleeve including the steps of: [0029](i) formation of a sleeve
body by providing one or more at least partially cured uniform layers on
a sleeve carrier; [0030](ii) formation of a relief image on the sleeve
body by imagewise jetting a curable jetting fluid; [0031](iii) optionally
overall post-curing; [0032]characterized in that between formation of
the sleeve body and formation of the relief image no polishing or
grinding is performed.

[0033]In the method according to a preferred embodiment of the present
invention a sleeve carrier is provided with one or more at least
partially cured uniform layers. The term uniform refers to surface
properties, evenness, smoothness, homogeneity, coating formulation, etc.
of the layers. Providing uniform layers eliminates the need for grinding
and/or polishing before formation of the relief image. Eliminating the
grinding and/or polishing steps shortens the time to prepare the
flexographic sleeve. Moreover, no additional apparatuses, including a
device to remove the "polymer dust" formed during grinding and polishing,
are needed in the method of the present preferred embodiment.

[0034]To obtain optimum quality prints, to avoid excessive wear of the
relief image during printing resulting in a poor runlength, it is very
important that the sleeve body has a perfect cylindrical shape. A
parameter often used in the flexographic art, reflecting the quality of
the cylindrical shape, is the Total Indicator Runout value, also referred
to as TIR value. Runout refers to the result obtained of placing the
cylinder on a spindle and rotating the cylinder about its central axis
while measuring with a dial indicator its surface deviation from perfect
roundness. Total Indicator Runout refers to such a measurement along the
length of the cylinder. More information on the Total Indicator Runout
parameter used in the flexographic industry and on methods to measure the
TIR value of a cylinder can be found in FLEXO® Magazine, February
2002 and "Flexography: Principles & Practices, 5th edition, Volume
6, page 128-143. Flexographic sleeve bodies are characterized by a TIR
value of typically 25 μm or less. These values are obtained by
grinding and/or polishing the sleeve body after applying the elastomeric
layers on the sleeve carrier. In a preferred embodiment of the present
invention, a sleeve body is provided, preferably by coating, more
preferably by vertical coating, on a sleeve carrier, one or more at least
partially cured layers. The TIR value of the sleeve body amounts to
preferably 100 μm or less, more preferably of 50 μm or less,
without performing any additional manipulation, such as grinding and/or
polishing.

Composition of the Uniform Layers

[0035]One or more curable compositions are applied onto a sleeve carrier,
forming the one or more uniform layers. If more than one curable layer is
formed, the layers may have the same or, more preferably, a different
composition. For example the layer nearest to the sleeve carrier may be
optimized towards an optimal adhesion between the "elastomeric floor" and
the sleeve carrier, while the layer, on which the relief image will be
jetted, may be optimized towards optimal adhesion between the relief
image and the "elastomeric floor".

[0036]The uniform layers are preferably polymerizable layers, which may be
cured by exposure to actinic or IR radiation or by electron beam
radiation. Curing may also be performed by applying heat to the coated
layers. Most preferably, the polymerizable layers may be cured by
exposure to UV light. Curing may be the result of crosslinking of
polymers, of polymerization of monomers and/or oligomers, or of both.

Initiators

[0037]The polymerizable layers according to a preferred embodiment of the
present invention may include one or more initiator(s). The initiator
typically initiates the polymerization reaction. The initiator may be a
thermal initiator, but is preferably a photo-initiator.

[0039]A photo-initiator produces initiating species, preferably free
radicals, upon absorption of actinic radiation. A photo-initiator system
may also be used. In the photo-initiator system, a photo-initiator
becomes activated upon absorption of actinic radiation and forms free
radicals by hydrogen or electron abstraction from a second compound. The
second compound, usually called the co-initiator, becomes then the
initiating free radical. Free radicals are high-energy species inducing
polymerization of monomers or oligomers. When polyfunctional monomers and
oligomers are present in the curable resin composition, the free radicals
can also induce crosslinking.

[0040]Curing may be realized by more than one type of radiation with
different wavelength. In such cases it may be preferred to use more than
one type of photo-initiator together.

[0041]A combination of different types of initiators, for example, a
photo-initiator and a thermal initiator may also be used.

[0042]Suitable photo-initiators are disclosed in e.g. J. V. Crivello et
al. in "Photoinitiators for Free Radical, Cationic & Anionic
Photopolymerisation 2nd edition", Volume III of the Wiley/SITA
Series In Surface Coatings Tecnology, edited by G. Bradley and published
in 1998 by John Wiley and Sons Ltd London, pages 276 to 294.

[0048]Suitable cationic photo-initiators include compounds, which form
aprotic acids or Bronstead acids upon exposure sufficient to initiate
polymerization. The photo-initiator used may be a single compound, a
mixture of two or more active compounds, or a combination of two or more
different compounds, i.e. co-initiators. Non-limiting examples of
suitable cationic photo-initiators are aryldiazonium salts,
diaryliodonium salts, triarylsulphonium salts, triarylselenonium salts
and the like.

[0049]Sensitizing agents may also be used in combination with the
initiators described above. In general, sensitizing agents absorb
radiation at a wavelength different then the photo-initiator and are
capable of transferring the absorbed energy to that initiator, resulting
in the formation of e.g. free radicals.

[0050]The amount of initiator in the curable composition of the present
invention is preferably from 1 to 10% by weight, more preferably from 2
to 8% by weight, relative to the total weight of the ingredients of the
polymerizable layers.

Curable Compounds

[0051]The polymerizable layers includes one or more curable compounds.
These curable compounds may include one or more polymerizable groups,
preferably radically polymerizable groups.

[0052]Any polymerizable mono- or oligofunctional monomer or oligomer
commonly known in the art may be employed. Preferred monofunctional
monomers are described in EP-A 1 637 322 paragraph [0054] to [0057].
Preferred oligofunctional monomers or oligomers are described in EP-A 1
637 322 paragraphs [0059] to [0064].

[0054]A particularly preferred curable compound is an urethane
(meth)acrylate oligomer. It has been found that the presence of urethane
(meth)acrylate oligomers, preferably in an amount of 40% by weight or
more, relative to the total weight of the ingredients of the
polymerizable layers, provides excellent printing properties to the
flexographic sleeves. The urethane (meth)acrylate oligomer may have one,
two, three or more polymerizable groups. Preferably the urethane
(meth)acrylate oligomers have one or two polymerizable groups.

[0056]Preferably, the polymerizable layers include also a silicone
acrylate compound, such as e.g. EBECRYL 1360.

[0057]To optimize the viscosity of the curable composition forming the
polymerizable layers, one or more mono and/or bifunctional monomers
and/or oligomers are used as diluents. Preferred monomers and/or
oligomers acting as diluents are miscible with the above described
urethane (meth)acrylate oligomers. Particularly preferred monomers and/or
oligomers acting as diluents do not adversely affect the properties of
the cured resin composition.

[0058]The monomer(s) or oligomer(s) used as diluents are preferably low
viscosity acrylate monomer(s).

[0062]Since excessive addition of these polymerization inhibitors will
lower the curing efficiency, the amount is preferably lower than 2% by
weight relative to the total weight of the ingredients of the
polymerizable layers.

Elastomers

[0063]To further optimize the properties of the flexographic printing
forme precursor the polymerizable layers may further include one or more
elastomeric compounds. Suitable elastomeric compounds include copolymers
of butadiene and styrene, copolymers of isoprene and styrene,
styrene-diene-styrene triblock copolymers, polybutadiene, polyisoprene,
nitrile elastomers, polyisobutylene and other butyl elastomers,
polyalkyleneoxides, polyphosphazenes, elastomeric polyurethanes and
polyesters, elastomeric polymers and copolymers of (meth)acrylates,
elastomeric polymers and copolymers of olefins, elastomeric copolymers of
vinylacetate and its partially hydrogenated derivatives.

[0064]The type and amount of monomers and/or oligomers and optionally the
elastomeric compounds are selected to realize optimal properties of the
printing forme precursor such as flexibility, resilience, hardness,
adhesion to the substrate and adhesion of the relief image. It may be
advantageous that the curable composition forming the outermost layer of
the "elastomeric floor" includes ingredients compatible with those of
curable compositions used to form the relief image by inkjet, to optimize
the adhesion between the relief image and the "elastomeric floor".

Plasticizers

[0065]Plasticizers are typically used to improve the plasticity or to
reduce the hardness of the flexographic printing forme precursor.
Plasticizers are liquid or solid, generally inert organic substances of
low vapor pressure.

[0067]Examples of particularly suitable plasticizers are paraffinic
mineral oils; esters of dicarboxylic acids, such as dioctyl adipate or
dioctyl terephthalate; naphthenic plasticizers or polybutadienes having a
molar weight of between 500 and 5,000 g/mol.

[0068]More particularly preferred plasticizers are HORDAFLEX LC50
available from HOECHST, Santicizer 278 available from MONSANTO, TMPME
available from PERSTORP AB, and PLASTHALL 4141 available from C. P. Hall
Co.

[0069]It is also possible to use a mixture of different plasticizers.

[0070]Preferred plasticizers are liquids having molecular weights of less
than 5,000, but can have molecular weights up to 30,000.

Other Additives

[0071]The polymerizable layers may further include other additives such as
dyes, pigments, photochromic additives, anti-oxidants, antiozonants and
tack-reducing additives. Examples of tack-reducing additives are for
example aromatic carboxylic acids, aromatic carboxylic acid esters,
polyunsaturated carboxylic acids, polyunsaturated carboxylic acid esters
of mixtures thereof. The amount of additives is preferably less than 20%
by weight based on the sum of all constituents of the photopolymerizable
composition, and is advantageously chosen so that the overall amount of
plasticizer and additives does not exceed 50% by weight based on the sum
of all the constituents.

Liquid Photopolymers

[0072]Commercially available liquid photopolymers, e.g. VERBATIM liquid
photopolymer resins from CHEMENCE, can be used to prepare the
"elastomeric floor". A wide range of liquid photopolymer products are
available, each product resulting upon coating and curing in layers
having particular properties, e.g. different Shore A hardnesses. When the
"elastomeric floor" is formed by more then one layer, different liquid
photopolymers may be used in each different layer. The curable
compositions used to form the uniform layers onto the sleeve carrier may
consist essentially of such a commercially available liquid photopolymer
and a photo-initiator, such as e.g. IRGACURE 127. Preferably, these
liquid photopolymers are used in combination with the diluent monomers
and/or oligomers described above to optimize the viscosity of the curable
composition.

Thickness of the Uniform Layers

[0073]The total thickness of the polymerizable layers may be chosen by the
skilled worker in accordance with the requirements of the desired
application. The total thickness may vary from 0.2 to 3.0 mm, more
preferably from 0.3 to 1.5 mm, most preferably from 0.4 to 1.2 mm.
Compared to conventional photopolymerizable layers applied on sleeves, to
be used in conventional flexographic sleeve formation whereby both the
"elastomeric floor" and the relief image is formed by the polymerizable
layers, the uniform layer(s) according to the present preferred
embodiment have a lower thickness because the layers are only used to
form the "elastomeric floor".

[0074]The "elastomeric floor" has preferably a Shore A hardness of from 30
to 80.

Curing of the Uniform Layers

[0075]After providing the polymerizable layers on a sleeve carrier, the
layer(s) are cured by irradiation or heat.

[0076]Heat may be used to cure (i.e. polymerize) when the composition(s)
includes a thermal initiator, as described above.

[0077]Irradiation may be electron beam irradiation or actinic irradiation,
preferably actinic irradiation. Curing with electron beam irradiation
does not necessitate the presence of an initiator in the curable
composition(s). The suitability of a particular actinic radiation source
is governed by the photo-sensitivity of the initiator used in preparing
the flexographic printing forme precursor. The preferred photosensitivity
of most common flexographic printing forme precursors is in the UV and
deep UV region of the spectrum.

[0079]UV radiation is generally classified as UV-A, UV-B and UV-C as
follows:

UV-A: 400 nm to 320 nm

UV-B: 320 nm to 290 nm

UV-C: 290 nm to 100 nm

[0080]It may be advantageous to use two radiation sources to perform the
curing. For example, the first UV source may be selected to be an UV-A or
UV-C radiation source while the second UV source may be selected to be an
UV-A or UV-C radiation source. The second curing step is often referred
to as a post curing step. Typically first an UV-A curing is performed,
followed by a UV-C post-curing, to obtain non-tacky surfaces.

[0081]However, in the method of preparing a flexographic sleeve according
to a preferred embodiment of the present invention, it has been observed
that a partially cured uniform layer, for example obtained by a short
UV-A curing without performing a UV-C curing, may result in an improved
adhesion with the relief image jetted on it. A possible explanation may
be the presence of unreacted monomers in the partially cured uniform
layer, which may cure together with the monomers of the jetted relief
image, upon overall curing.

[0082]When more than one layer of curable compositions are provided on a
substrate, curing may be performed after providing all of the layers on
the substrate or curing may be performed after each layer has been
provided on the substrate. When more or more layers are present,
partially curing the outermost layer may be beneficial towards the
adhesion of the relief image on it.

[0083]The curing time will vary depending on the intensity and spectral
energy distribution of the radiation, the distance between the light
source and the printing element, the composition and thickness of the
curable composition(s) of the printing forme precursor.

[0084]A removable coversheet may be present during curing, to minimize the
inhibition of the polymerization by oxygen. Another method to minimize
the inhibition by oxygen is performing the curing under inert N2 or
CO2 atmosphere.

[0085]Any method may be used to form a sleeve body by applying one or more
at least partially cured uniform layers on a sleeve carrier, with the
proviso that no grinding and/or polishing step is needed before forming
the relief image by inkjet on the sleeve body.

Vertical Coating Device

[0086]A particularly preferred method for applying one or more at least
partially cured layers on a sleeve carrier is disclosed in the
unpublished EP-A 06 120 823 (filed 18, Sep. 2006). EP-A 06 120 823
discloses a "vertical" coating device that supports a wide range of
sleeve carriers, and is capable of coating a single or a multitude of
"uniform" layer(s) of curable material onto a sleeve carrier, with a
coating layer thickness variable between several micrometers and several
millimetres. The uniformity of the coated layer(s) is provided through at
least partial curing of the layer(s) immediately after or almost
simultaneously with coating.

[0087]Because one application of a preferred embodiment of the present
invention is the coating of an UV-curable material onto a sleeve carrier,
the discussion below will often refer to UV-curable coating liquids,
UV-LED's, etc. to illustrate the present invention. However, it should be
understood that the present invention is not limited to UV light or UV
photocuring technologies. Electron beam radiation, IR radiation or heat
may also be used to at least partially cure the one or more layers
provided on the sleeve carrier or core.

[0088]Preferred embodiments of the invention may be engrafted on any
equipment suitable for positioning a sleeve carrier in a vertical
position and having a tool smoothly moveable along the sleeve carrier in
the vertical direction. Examples of such equipment are vertical ring
coaters described in the prior art or commercially available from Max
Daetwyler Corporation (Switzerland), the Stork Prints Group (The
Netherlands), and others. The description of the present invention will
therefore not elaborate on the basic features of this type of equipment.
Only in summary, a vertical ring coater as shown in FIG. 1 may include a
vertical support column 1 that supports the sleeve carrier 8 in a
vertical position, incorporates a mechanism 4 for lifting and lowering a
coating carriage 5 vertically along the sleeve carrier 8, and provides a
space envelope for integrating a number of utilities such as power
cabling etc. The coating carriage 5 supports a coating collar 6 that is
filled with a coating liquid for coating onto the sleeve carrier 8. The
sleeve carrier 8 is mounted in the vertical position by flanges or
mounting heads 9 at both ends; the flanges or mounting heads 9 themselves
are supported on the vertical support column 1. The flanges or mounting
heads 9 may be shaped so as to provide a smooth extension of the sleeve
carrier's peripheral surface, thereby allowing coating of the sleeve
carrier 8 up to edges and also providing a sealed home position for the
annular coating collar 6 at one of the flanges or mounting heads 9. The
sleeve carrier 8 may be coated during an upward or downward movement of
the coating collar 6.

[0089]When the coating collar 6 moves downwards during the coating
process, the coating layer is created from the meniscus between the
liquid surface of the coating liquid contained in the coating collar 6,
and the peripheral surface of the sleeve carrier 8. In general, the
thickness of the coating layer applied with this type of immersion
coating technique is determined by the formula

d = 20 * η * v f ( Eq . 1 ) ##EQU00001##

wherein d equals the thickness of the coated layer in μm, η is the
viscosity of the coating liquid in mPas, ν is the coating velocity in
mmin-1, and f is the specific density in kg/liter.

Annular Irradiation Stage

[0090]A preferred embodiment of the invention is now described in detail,
with reference to FIG. 2. The coating collar 21 in FIG. 2 includes an
annular squeegee 22 providing a slideable seal between the bottom of the
coating collar 21 and the sleeve carrier 13, in order to prevent a
coating liquid 24 contained in the coating collar 21 to leak from the
coating collar 21. The coating collar 21 is open at the top. The liquid
surface 25 of the coating liquid 24 contained in the coating collar 21
forms an annular meniscus 26 with the peripheral surface of the sleeve
carrier 13. The coating collar 21 may be supported by a coating carriage
(e.g. coating carriage 5 in FIG. 1) that is connected to a lifting and
lowering mechanism (e.g. lift mechanism 4 in FIG. 1) incorporated in a
vertical support column (e.g. column 1 in FIG. 1). These features have
been omitted in FIG. 2. The lifting and lowering mechanism can move the
entire coating stage 11, i.e. the assembly of the coating carriage with
the coating collar, up and down along a vertical axis. When a sleeve
carrier 13 is mounted, the lifting and lowering mechanism is capable of
moving the annular coating stage 11 along the peripheral surface of the
sleeve carrier 13, providing a coating meniscus 26 at the top and a
sealing contact at the bottom of the coating collar 21. The coating axis
10 refers to the vertical axis through the centre of the coating collar
21 and coinciding with the axis of the sleeve carrier 13 when mounted on
the coating device. The coating collar 21 moves up and down, centred
around the coating axis 10.

[0091]On top of the annular coating stage 11, an annular irradiation stage
12 is mounted. The purpose of the irradiation stage 12 is to set the
coated layer, just applied by the annular coating collar 21, and prevent
the coating liquid from running down. Running down of the coated layer
decreases the layer thickness at upper locations and increases the layer
thickness at lower locations along the sleeve carrier 13, and decreases
the topographic uniformity of the layer and therefore the quality of the
applied coating. It is therefore an advantage to "freeze" the coated
layer right after application onto the sleeve carrier 13. The term
"freeze" does not necessarily imply a full setting of the coated layer; a
partial setting of the layer to prevent run-down of the coating liquid
from the sleeve carrier 13 is sufficient to provide a uniform layer of
coating material.

[0092]In a preferred embodiment, the irradiation stage 12 may be
360° all around and based on the use of UV LEDs and concentrating
or collimating optics. UV LED's have several advantages compared to UV
arc lamps, such as their compactness, acceptable wavelength and beam
stability, good dose uniformity and a large linear dose regulation range.
A disadvantage of the UV LED's is their relative low power output. UV
LEDs however are relatively small and can be grouped together in such a
way that their combined power is sufficient to cover the required UV
curing range for different types of coating liquids, different
thicknesses of coating layer, different sleeve diameters (i.e. distance
from UV LED to peripheral surface of the sleeve), etc. A cross-sectional
view of a first embodiment of an annular irradiation stage is shown in
FIG. 3. The irradiation stage is construed around an array of LEDs 31, a
Fresnel lens 32 with reflector 33 and collimating mirror 34. The role of
the optics is twofold: firstly Fresnel lens 32 with reflector 33
concentrates the light from the array of LEDs 31 into the focal point of
the collimating mirror 34, and secondly the collimating mirror 34
collimates the light from the array of LEDs 31 into parallel horizontal
beams for irradiating the coated layer on the sleeve. Revolving this
optical setup 360° around the coating axis provides radiation from
an annular radiation source, i.e. an annular LED array, which is
substantially collimated in the horizontal direction and substantially
focused onto the coating axis 10, as illustrated by the arrows in the
lower part of FIG. 2. A cross-sectional view of a second embodiment of an
annular irradiation stage is illustrated in FIG. 4 and shows a LED 41
positioned at the focal point of a parabolic reflecting cavity 44 of
collimator base 40. A heat sink 45 for removing heat from the LED 41 is
integrated in the collimator base 40. The small size of the LED 41 allows
it to be positioned in the focal point of the parabolic reflecting cavity
44 without creating substantial voids in the collimated output beam.
Revolving this optical setup 360° around the coating axis results
in an annular radiation source and annular collimating optics for
providing annular radiation as explained above. The radiation energy
contained in the collimated beam can be easily modulated, by adjusting
the radiation intensity, so as to accommodate for the variation in
distance or diameter of different sleeve carriers, as well as for
variations in formulation of the coating liquid.

[0093]The result is a radiation beam with large beam uniformity, high beam
stability, wide range of beam intensity adjustment (LEDs can be dimmed to
a few % of their maximal output power or can be time modulated), and
precise UV curing control through ease of calibration. The advantages
are: (i) no extra mechanical adjustments required when changing sleeve
carriers of different sleeve carrier diameters--short sleeve carrier
change over time, (ii) irradiation power adaptable--no power loss, and
(iii) uniform beam properties for accurate and uniform curing--combined
quality and speed aspects.

[0094]The annular shape of the UV LED array 41 and associated collimating
optics 44 of the irradiation stage 12 allows a uniform annular
irradiation of the coated layer. Furthermore, its compactness and low
weight allow the annular irradiation stage 12 to be fixedly mounted on
the annular coating stage 11. In operation, the annular irradiation stage
12 then moves along with the annular coating stage 11 and only one drive
mechanism for moving the assembly up and down the sleeve carrier 13 is
required.

[0095]Certain applications may require the use of a multitude of
irradiation stages 12, mounted in cascade, for providing radiation with
different wavelengths, at different distances from the coating stage 11,
providing different radiation power, etc. The multitude of irradiation
stages may be mounted on top of each other as one assembly, which itself
may be mounted onto the coating stage 11. Mechanically linking the stages
together is not mandatory. It is however preferred that the stages be
moveable up and down the sleeve carrier in a synchronized way.

[0096]Notwithstanding the movement of the coating stage 11 and possible
disturbances of the liquid surface 25 in the coating collar 21,
experiments show surprisingly that the coated layer, applied with a
coating device as described above, is of very good homogeneity and
surface evenness.

Rotating Irradiation Stage

[0097]If however the irradiation stage is not all around annular, but
includes one or more distinct circular irradiation sectors, one or more
linear irradiation segments or singular irradiation units, the invention
requires the irradiation stage to spin around the sleeve carrier in order
to achieve a uniform irradiation all around the coated layer. This is
illustrated in FIG. 5. Four singular irradiation units 50 are shown
equably arranged around the coating axis 10. Each irradiation unit 50 may
include an UV LED 51 and collimating paraboloidal optics 54 to produce a
beam of collimated parallel UV light. A detailed description of one
embodiment of a singular irradiation unit 50 may be found in granted U.S.
Pat. No. 6,880,954. The singular irradiation units 50 may be mounted on a
mounting base 59 of the irradiation stage 52. In order to provide all
around uniform irradiation of the coated layer on the periphery of a
sleeve carrier 13, the mounting base 59 rotates around the coating axis
10 while coating is performed, i.e. while the coating stages 11 moves
vertically coaxial with the coating axis 10. Therefore the mounting base
59 is rotatably mounted on the coating stage 11 by e.g. an annular guide
58, and driven by a motor 56 and gear transmission 57 mounted on the
coating stage 11. The gear transmission 57 may include a gear wheel
cooperating with a crown gear mounted on the mounting base 59, but other
transmission systems may be used as well such as bevel gears. The
mounting base 59 of the irradiation stage 52 further includes multiple
rotational electrical connectors 55, e.g. slip rings, for powering the
multiple singular irradiation units 50 on the mounting base 59.
Mechanical and electrical drives and interconnections between the
irradiation stage 52 and the coating stage 11, e.g. the motor 56, the
annular guide 58, the gear transmission 57 and the electrical slip
connections 55, preferably are mounted onto or refer to the coating
carriage 29 of the coating stage 11. This setup allows exchangeability of
the annular coating collar 21 to adapt for different external diameter of
the sleeve carriers to be coated, without requiring a change in the
mechanical and electrical setup of the assembly of the coating stage 11
and the rotatable irradiation stage 52. The embodiment of a rotatable
irradiation stage 52 has been illustrated in FIG. 5 with four singular
irradiation units 50. As indicated above the rotatable irradiation stage
may include other irradiation units such as irradiation segments based on
a linear array of LEDs and a concentrating and collimating mirror, or
they may include arc lamp systems although these are generally more
complex and heavier to mount, connect and rotate. The rotation of the
irradiation stage provides a 360° integration function for the
radiation from the different irradiation units and smoothens the
radiation intensity variations between different irradiation units and
within each irradiation unit. An equable distribution of the irradiation
units around the coating axis may be a preferred setup, but it is not
required because the rotation of the irradiation stage will provide a
360° integration anyhow. A rotatable irradiation stage may
therefore also be realized using only one singular irradiation unit.

Further Embodiments Details or Alternatives

[0098]In the embodiments described so far the irradiation source, e.g. an
individual LED or an annular LED array, was linked to a corresponding
collimating optics, e.g. a paraboloidal reflector respectively an annular
collimating optics, and was considered one assembly. In an alternative
embodiment the optics may be omitted in which case the LED radiation
source directly irradiates the peripheral surface of the coated sleeve
carrier. Rotation of the irradiation source may provide additional
integration and averaging of the radiation energy. In another alternative
embodiment a non-rotating annular collimating optics may be combined with
a rotating radiation source. In this configuration, the radiation source
orbits between the peripheral surface of the coated sleeve carrier and
the annular collimating optics.

[0099]From Eq.1 we know that the viscosity of the coating liquid is an
important parameter in controlling the thickness of the applied layer. It
is therefore preferable to shield the coating liquid in the coating
collar from any sources that may have a direct or indirect impact on the
viscosity of the coating liquid. In radiation curable systems, the
viscosity of a liquid is made controllable via exposure to radiation,
i.e. the change the viscosity of a coated layer in order to freeze, set
or cure the coated liquid is controlled via exposure to radiation. The
coating device according to a preferred embodiment of the invention
therefore preferably includes a radiation lock positioned between the
radiation stage and the coating stage, and moveable therewith, for
shutting off direct and indirect, e.g. scattered, radiation of the
radiation source from the coating liquid contained in the coating collar.
The radiation lock is preferably annular shaped and may for example be
realized by providing a cover to the coating collar reservoir. A more
advanced radiation lock would be an adjustable iris diaphragm as used in
optics, the diaphragm opening being adjusted to be slightly larger than
the diameter of the sleeve carrier to be coated. The annular radiation
lock may be mechanically integrated in the coating stage, in the
irradiation stage or as a separate unit in between both stages.

[0100]In applications using free radical UV curable liquids, it is known
that the curing, in some cases, may be retarded or even non-existent due
to the presence of oxygen in the cure zone. In this case, an inerted
atmosphere may be used to enhance the cure capabilities. When related to
UV curing, the term `inerted` simply means the elimination in ideal
situations or, more appropriately, the minimizing of the amount of
inhibiting oxygen at the surface of the coating within the UV cure zone.
In a vertical coating device according to a preferred embodiment of the
invention, the cure zone refers to the area surrounding the coated layer
on the peripheral surface of the sleeve carrier that is exposed to the
radiation from the irradiation stage. An inertization environment may be
created by (i) adding a gas such as nitrogen, argon or carbon dioxide to
the atmosphere in the cure zone and especially close to or at the surface
of the coated layer, and (ii) minimizing the possibility of ingress of
air, a.o. through a drag effect resulting from the relative movement
between the coated layer and the irradiation stage, in that zone.

[0101]Adding an intertization gas, such as nitrogen, argon or carbon
dioxide, to the atmosphere in the cure zone may be accomplished by use of
an annular manifold, connected with flexible tubing to a source of
intertization gas housed in the vertical support column of the coating
device. Annular clearance seals at both ends of the cure zone, i.e. at
the upper and lower end of the irradiation stage, with a small clearance
to the peripheral surface of the coated sleeve carrier may be used to
prevent the inertization gas from flowing out of the cure zone. These
seals preferably have an adjustable inner diameter to fit with a small
clearance to the various sleeve carrier diameters. Iris diaphragms may be
suitable seals for this purpose. A controlled flow of inertization gas
within the cure zone may be realized when using two manifolds, i.e. an
inlet and outlet manifold.

[0102]The ingress of air in the cure zone is likely to occur at the lower
end of the cure zone when the coating stage moves downward during the
coating process, that is, from between the coating stage and the
irradiation stage. Counteracting the air intake may be realized by an
annular blow knife at the lower entrance of the curing zone, i.e. between
the irradiation stage and the coating stage. The annular blow knife,
moving along between the coating stage and the irradiation stage, may be
connected with flexible tubing to a source of inertization gas housed in
the vertical support column of the coating device.

[0103]Adding a "closed" inertization environment to the irradiation stage
has been described for oxygen inhibition in free radical UV curing
systems. Depending on the coating formulation and the way the coated
liquid layer is surface-cured, other embodiments of an intertization
environment may be thought of.

[0104]Instead of providing and integrating a series of supplementary tools
in and around the moveable irradiation stage to create an inertization
environment in the cure zone, the entire coating device may be capped to
close off the device from the ambient environment, in which case the task
of creation of an intertization environment within the coating device is
much simpler. Alternatively, the entire coating device may be installed
in an inert environment provided by the end user.

LED Technology

[0105]An advantage of using LED technology for irradiating the coated
layer is that the radiation intensity, and therefore the amount of
radiation energy received by the coated layer, is easily adjustable. In
one example the radiation intensity may be adjusted as a function of the
coated layer thickness or a corresponding process variable (see Eq.1
above), e.g. the radiation intensity may be adjusted as a function of the
viscosity of the applied coating liquid or the coating speed. In another
example the radiation intensity may be adjusted as a function of the
coating formulation or a component in the coating formulation, e.g. the
UV LED power may be adjusted as a function of the amount of
photo-initiators or sensitizers included in a UV coating liquid. In still
another example the radiation intensity may be adjusted as a function of
the optical distance between the radiation source and the peripheral
surface of the coated sleeve carrier, e.g. the received radiation energy
per unit area on the peripheral surface of the coated sleeve carrier in
FIG. 2 varies with the sleeve carrier diameter and may be calculated and
compensated for by adjusting the radiation intensity or power of the
LEDs.

[0106]Compared to alternative radiation technologies such as for example
arc lamps sources, LED technology provides the advantage of a small
footprint and good beam and wavelength stability.

[0107]A further advantage of LED technology is their narrow bandwidth and
singular spectral output, and the possible choice of a mixture of
different spectral output UV LEDs. This choice of single wavelength UV
output or a combination of spectral outputs allows for the further
process tuning of the UV curing and of the coating chemistry, now mainly
centred in the UVA and UV Visible ranges. A combination of spectral
outputs can easily be selected at random by the mere ON and OFF switching
of banks of different UV LED spectral output. Furthermore, the nearly
complete absence of any IR radiation of these UV LEDs eliminates the need
for IR-absorption filters, such as water-filled reservoirs, and is a
bonus in reducing local and uneven subject heating.

[0108]Still further advantages of LED technology are its compactness, low
weight and the ongoing technological trend towards higher power LEDs.

Laser Curing

[0109]An alternative embodiment of a coating device according to the
invention is shown in FIG. 6 and may include a rotating irradiation stage
with a laser beam 64 as a single rotating irradiation unit. The laser
beam 64 may be provided from a fixed laser source 60 above the sleeve
carrier 13, possibly mounted onto the coating device's vertical support
column (see FIG. 1). For that purpose, the sleeve carrier is single-ended
mounted via the bottom flange or mounting head of the coating device. The
laser source 60 may be mounted coaxial with the coating axis 10 for
creating a laser beam 64 starting off along the coating axis 10. A
spinning optical path is provided for guiding the fixed laser beam
starting off at the laser source 60 to a spinning mirror 63 used for
directing the laser beam onto the peripheral surface of the sleeve
carrier 13. In the embodiment shown in FIG. 6, the spinning optical path
is created via a rotating central mirror 61 deflecting the starting laser
beam 641 in a direction perpendicular to the coating axis 10 and
spinning the laser beam around the coating axis 10. A first spinning
mirror 62, co-operating with the rotating central mirror 61, deflects the
spinning laser beam 642 parallel with the coating axis but at the
outside of the sleeve carrier. Finally, a second spinning mirror 63 that
is part of the rotating irradiation stage 52 co-operates with the first
spinning mirror 62 and deflects the spinning laser beam 643 towards
the coating axis 10 thereby projecting laser beam 644 in a spinning
way onto the coated layer on the peripheral surface of the sleeve carrier
13. The synchronization of the multiple co-operating mirrors 61-62-63 may
be realized by fixing their angular position via a mechanical framework
65-66 attached to the mounting base 59 of the rotating irradiation stage
52. The framework 65-66 therefore spins along with the irradiation stage
52. The spinning of the laser beam 64 is therefore completely controlled
by and synchronized with the rotation of the irradiation stage 52.

[0110]In a preferred embodiment, as shown in FIG. 6, a vertical guiding
system 67 may be installed to keep the rotating framework element 66, and
mounted thereon central mirror 61 and first spinning mirror 62, at a
fixed height while the coating stage 11 and spinning irradiation stage 52
are moving up and down during a coating operation. If the vertical
position, i.e. the height, of the rotating framework element 66 is fixed
via for example a mechanical reference or link to the coatings device's
vertical support column, the vertical guiding device 67 may include
simple bearings. If the vertical position, i.e. the height, of the
rotating framework element 66 is not fixed with a mechanical reference,
the vertical guiding system 67 preferably include an active linear motion
system (not shown) driven to keep the rotating framework element 66 at a
fixed vertical height independent of a vertical movement of the coating
stage and irradiation stage. The main advantage of the vertical guiding
system 67 is to reduce the required installation height for the coating
device.

[0111]In another embodiment the rotating framework element 66 may be
mounted completely independent from the coating/irradiation stage. The
spinning framework elements 65 and vertical guiding system 67 may then be
omitted. However the rotation of the irradiation stage and the framework
element 66 still needs to be synchronized in order to preserve the
spinning optical path that guides the laser beam 64 onto the peripheral
surface of the sleeve carrier 13. The coating device may then include two
synchronized independent spinning entities.

[0112]In order to avoid collision of the spinning framework elements 65
with the mechanism for lifting and lowering the coating carriage, the
lifting and lowering mechanism as illustrated in FIG. 1, integrated in
the peripheral vertical support column, preferably is replaced by a
linear motion system operating completely within the space envelope of
the spinning framework element 65. Telescopic lift systems operating
within this space envelope may for example be used.

[0113]The above disclosed preferred embodiments of the invention are
described with reference to a laser system. The inventive concept however
is not limited thereto and in general includes the use of a fixed mounted
radiation source linked to a spinning optical path to guide the radiation
beam from the fixed radiation source all around the peripheral surface of
the sleeve carrier in synchronism with the vertical coating movement of a
coating stage. Any radiation source that provides the required type of
radiation, with enough power to at least partially cure the coated layer
on the peripheral surface of a sleeve carrier, may be used.

Different Sleeve Carrier Sizes

[0114]It has been mentioned in a previous section that the radiation power
may be adjusted as a function of the optical distance from the
irradiation source to the peripheral surface of the sleeve carrier, such
that adequate curing or "freezing" of the coated layer onto the
peripheral surface of the sleeve carrier is achieved. This improves the
compatibility of the irradiation stage with different sleeve carrier
diameters. It is especially advantageous when the irradiation stage
configuration is fixed and wherein the irradiation units are positioned
outside a cylindrical space envelope around the coating axis occupied by
the largest sleeve carrier diameter within a range of different sleeve
carrier diameters. Alternatively, when the irradiation stage
configuration is adjustable, the radial position of individual
irradiation units from the coating axis, i.e. their radial coordinate in
a polar coordinate system around the coating axis, and/or the spinning
velocity of these units around the coating axis may be adjusted in order
to keep the radiation energy received per unit area on the peripheral
surface of sleeve carriers of different diameters constant.

[0115]Regarding the operation of the coating stage with different size
sleeve carriers, the coating meniscus and the annular seal are important
issues. The annular seal around the peripheral surface of the sleeve
carrier prevents leakage and run down of coating liquid from the coating
collar. When changing sleeve carrier diameter, either the entire coating
collar (including the annular seal) may be replaced by another suited for
the new sleeve carrier diameter or only the annular seal may be replaced
or adjusted to fit with the new sleeve carrier diameter. If the annular
seal is realized as an iris diaphragm of which the aperture is adjustable
within a range, no replacement parts are required when changing the
sleeve carrier diameter, provided that the sleeve carrier diameter falls
within the range of the adjustable aperture. If the annular seal is
removeably attached to the coating collar, a seal with a different fixed
internal diameter may be used. The range of annular seal internal
diameters that can be used with a coating collar is determining the
maximum and minimum sleeve carrier diameter that can be coated with that
coating collar.

[0116]Preferably that coating stage and the irradiation stage are designed
to support the same range of sleeve carrier diameters so that both
modules can be pre-assembled as a tandem and be inserted or replaced as
one assembly.

Drive Systems & Process Control

[0117]In the embodiments described above, the irradiation stage or
multitude of irradiation stages are mounted on top of the coating stage
and move together with the coating stage as a single "coating assembly".
From a mechanical point of view, this provides the advantage that only
one lifting and lowering mechanism is required to operate the vertical
coating device, whereas from an electrical point of view, all electrical
connections to the "coating assembly" may be provided through a single
cable carrier between the stationary vertical support column and the
moving "coating assembly".

[0118]Obtaining a coated layer onto sleeve carriers with a controlled and
uniform thickness, using one of the coating devices described above, may
be difficult to achieve without any feedback regarding the irradiation
dose and irradiation uniformity effectively applied to the coated layer.
Therefore an energy dose controlling system may be added to the "coating
assembly" for measuring the effective curing rate of the applied layer
and adjusting the applied energy dose, spinning velocity (if applicable)
and/or coating speed in a closed loop system. A near-infrared
spectrometer may for example be used to measure the degree of UV or EB
curing, i.e. the curing rate, of the coated layer.

[0119]However, if the purpose of the irradiation stage is to only
partially set the coated layer to prevent run-down of the coating liquid
from the sleeve carrier, the irradiation dose is less critical and
monitoring of the irradiation dose in a closed loop system may not be
required. A calibration of the irradiation stage combined with open loop
control may be sufficient.

[0120]A full cure of the coated layer may be provided off-line using
existing sleeve processing devices or may be provided in-line using an
additional radiation systems as disclosed in Japanese patent application
JP 54-014630. A full cure of the coated layer may also be realized by
adding radiation capacity to the existing irradiation stage. The
additional capacity may be provided by increasing the radiation power
(e.g. additional UV LED arrays), adding different radiation sources (e.g.
adding deep cure UVA wavelength radiation to the surface cure UVC
radiation), specially adapted collimating optics delivering a variable
irradiation intensity as a function of the vertical distance to the
coating meniscus (e.g. a radiation source with a collimating optics
providing a concentrated high irradiation intensity close to the coating
meniscus, to achieve surface curing of the coated layer, and a vertically
spread out lower irradiation intensity further away from the coating
meniscus, to realize deep curing of the coated layer), or by
straightforward duplicating existing irradiations stages.

Operation

[0121]The coating device according to a preferred embodiment of the
invention may be set up and prepared for coating operations without the
presence of a sleeve carrier. Thereto, one of the flanges or mounting
heads, for mounting the sleeve carrier onto the coating device, may be
used to provide a home position to the coating assembly. The flange or
mounting head providing this home position has a similar or slightly
smaller external diameter than the diameter of the sleeve carriers
intended to be used with the flange or mounting head. When the coating
assembly is in its home position, the annular seal of the coating collar
may be adjusted to fit with the sleeve carrier diameter, even prior to
mounting the sleeve carrier in the coating device, and the coating collar
may be filled with a coating liquid, without leakage. The coating stage
is then ready for coating operations.

[0122]If flanges or mounting heads are used with substantially different
external diameter than the diameter of the sleeve carriers to be coated,
the preparation of the coating assembly cannot be performed without the
presence of a sleeve carrier mounted on the coating device. A home
position for the coating assembly should then be provided by the sleeve
itself. This is however not a preferred situation as it requires
additional care and setup of the coating collar with each change of
sleeve carrier.

[0123]After preparing the coating assembly and mounting the sleeve carrier
on the coating device, the lifting and lowering mechanism moves the
coating assembly to a start position with the coating meniscus close to
or just past an end of the sleeve carrier, depending on the type of
flange or mounting head used. The coating process preferably starts at
the upper end of the sleeve carrier and continues in a downward direction
to the lower end of the sleeve carrier while the lifting and lowering
mechanism moves the coating assembly downwards. As the coating assembly
moves downward, the irradiation stage follows immediately after and
irradiates the just coated layer to cure at least the surface of the
coated layer, which prevents run down of the applied coating liquid. If a
spinning irradiation stage is used, the irradiation stage not only
follows the coating meniscus at a fixed distance, but in addition spins
around the sleeve carrier to generate a uniform 360° irradiation
of the coated layer. At the end of the coating process, the lifting and
lowering mechanism halts the coating assembly with the coating meniscus
close to or just past the lower end of the sleeve carrier, depending on
the type of flange or mounting head used. If the flanges or mounting
heads allow end-to-end coating of the sleeve carrier, the coating
assembly will move that far downward to allow the irradiation stage to
irradiate the coated layer up to the lower end of the sleeve carrier. The
thickness of the coated layer may be controlled via the velocity of the
coating assembly moving downward, the viscosity of the coating liquid or
the number of successive coating operations applied (see hereinafter).
After the coating process, the coating assembly is left at its position
against the lower or upper flange or mounting head and the coated sleeve
may be removed without special care for the coating collar.

[0124]Alternatively, a coating layer may be applied while the coating
assembly moves upward, in which case the coating mechanism is a squeegee
type coating mechanism, instead of the immersion type coating during a
downward movement of the coating assembly as described above. Application
of a coating layer during upward movement of the coating assembly may
require an irradiation stage positioned below the coating stage and
moving together with the coating stage to cure at least the surface of
the squeegee coated layer. Squeegee type coated layers, associated with
an upward movement of the coating collar, may be thinner than immersion
type coated layers, associated with a downward movement of the coating
collar. Unfortunately there is no formula, analogous to Eq.1, known to
the inventors to predict the thickness of the squeegee type coated layer.
Each of the alternatives may therefore have advantages in specific
applications.

[0125]The coating device may also operate in a multiple pass mode with
intermediate "curing" of the surface of each of the applied layers. The
coating may be mainly bidirectional or unidirectional as will become
clear from the following.

[0126]A multiple pass operating mode may include the steps of applying a
first immersion coated layer while moving a coating assembly downward and
curing at least the surface of the first immersion coated layer with an
upper irradiation stage positioned above and moving with the coating
stage; then moving the coating assembly upward while applying a first
squeegee coated layer and optionally curing at least the surface of the
first squeegee coated layer with a lower irradiation stage positioned
below and moving with the coating stage; afterwards applying a second
immersion coated layer while moving the coating assembly downward and
curing at least the surface of the second immersion coated layer with the
upper irradiation stage moving with the coating stage, etc. As the
annular squeegee of the coating collar is designed to prevent leakage of
coating liquid from the coating collar at the sliding contact between the
coating collar and the sleeve carrier, the thickness of the layer applied
via a squeegee type coating during an upward movement of the coating
assembly typically is significantly less than the thickness of the layer
applied by the immersion coating during the downward movement of the
coating assembly. In this case, there is a main (immersion) coating
action during the downward movement of the coating assembly and a
fractional (squeegee) coating action during the upward movement thereof.
The coating is primarily unidirectional. Intermediate curing of the
fractional (squeegee) coating layer may therefore not be necessary as it
will merge with the significantly thicker subsequent main (immersion)
coating layer from a subsequent coating action during a downward movement
of the coating assembly. The immersion coated layer is of course
irradiated using the upper irradiation stage. So, a multiple pass coating
device according to a preferred embodiment of the invention not
necessarily includes an upper and a lower irradiation stage to cure at
least the surface of the coated layer in both coating directions; a
single irradiation stage linked with a main coating direction may serve.

[0127]Multiple pass operation of the coating device as described may be
used for applying uniform thick layers of coating material onto sleeve
carriers. It may for example be used in cases where physico-chemical
parameters of the coating liquid, e.g. viscosity, or limitations of the
coating device, e.g. coating velocity, would limit the thickness of a
coated layer as predicted from Eq.1 to a value below what is functionally
required for the application.

[0128]Multiple pass operation of the coating device may also be used for
applying a multitude of layers of different coating liquid formulations.
The coating liquids may have different physicochemical properties, e.g.
viscosity, or the corresponding coated layers may have different
physicochemical or mechanical properties such as compressibility,
hardness, wear-resistance, wettability.

[0129]E.g. for the production of an optimized "elastomeric floor" on the
sleeve carrier, to be used in the method according to a preferred
embodiment of the present invention, it may be desirable to provide
compressible lower layer(s) (suitable for absorbing for example the
unevenness in corrugated board printing material) and upper layer(s)
optimized towards adhesion with the inkjetted relief image (for increased
durability and suitable for longer print runs). If desired a complete
physicochemical thickness profile may be created for the coated
multilayer.

[0130]The flanges or mounting heads may require regular cleaning to remove
coating liquid residues from end-to-end coating processes or linked with
their use as home position for the coating collar. A coating liquid
repelling layer on the flanges or mounting heads may facilitate this
cleaning.

[0131]Only if a different size of sleeve is to be coated, different
flanges or mounting heads may be installed and the annular seal of the
coating collar may be changed or adjusted to match with the new sleeve
carrier diameter. An example of an adjustable annular seal is an
adjustable iris diaphragm including overlapping sealing leaves wherein
the diaphragm opening, i.e. the aperture, is adjustable through
adjustment of the position of the leaves relative to each other, as known
in photography. The higher the number of leaves in the iris diaphragm,
the better the sealing property of the iris diaphragm around the
peripheral surface of the sleeve.

Forming the Relief Image by Inkjet

[0132]The relief image is formed on the one or more, at least partially
cured uniform layer(s) of the sleeve body. Any known inkjet method to
build 3D images may be used, in particular those described in EP 1 428
666, EP 1 437 882 and EP 1 637 322.

[0133]In a first step, the sleeve body provided with the one or more at
least partially cured layers is mounted on a cylindrical axe of a 3-D
inkjet printer. If the diameter of the sleeve body is too large to fit on
the cylinder of the 3D inkjet printer, a so called bridge sleeve,
positioned between the cylinder and the sleeve body, may be used.

[0134]The relief image is formed by imagewise jetting at least two layers
of a curable jetting fluid on the sleeve body. Preferably, each imagewise
jetted layer of a curable jetting fluid is at least partially cured, to
immobilize the jetted droplets, before jetting the subsequent layer.
However, curing may also be performed on more than one subsequently
jetted layers of a curable jetting fluid.

[0135]The layers forming the relief image may all be formed with the same
curable jetting fluid, alternatively the layers forming the relief image
may be formed with at least two different curable jetting fluids. For
example, the layers forming the top of the relief image may be formed
with curable jetting fluids, resulting upon curing in layers having a
higher Shore A Hardness than the layers forming the bottom of the relief
image, for example to increase the run length of the printing forme. Or,
the layers forming the top of the relief image may be formed with curable
jetting fluids, resulting upon curing in layers having optimal printing
properties. Alternatively, the layers of the relief image nearest to the
sleeve body may be formed with curable jetting fluids, resulting upon
curing in an optimized adhesion between the relief image and the sleeve
body.

[0136]Alternatively, curable jetting fluids having a different composition
may be used within one layer of the relief image. For example, small
printing areas may be formed with curable jetting fluids, resulting upon
curing in a higher Shore Hardness, whereas large printing areas may be
formed with curable jetting fluids, resulting upon curing in a lower
Shore Hardness.

[0137]The method according to a preferred embodiment of the present
invention enables the formation of flexographic sleeve formes, i.e. the
"elastomeric floor" and the relief image consecutively within a limited
time frame and close to the printing press.

[0138]As mentioned above, improved adhesion of the relief image to the
"elastomeric floor" may be realized by partially curing the "elastomeric
floor". However, the improved adhesion may diminish when the time between
partially curing the "elastomeric floor" and forming the relief image on
it by inkjet becomes too long, depending on the storage conditions of the
sleeve body, i.e. humidity, temperature and lightning conditions.
Preferably, the relief image is formed within 24 hours, more preferably
within 12 hours after providing the one or more at least partially cured
uniform layer on the sleeve body.

Curable Jettable Liquid

[0139]The curable jettable liquid suitable for the method for preparing a
flexographic printing sleeve forme according to a preferred embodiment of
the present invention preferably contains at least four components: (i) a
monofunctional monomer, (ii) a polyfunctional monomer or oligomer, (iii)
a plasticizer and (iv) a photo-initiator. The curable jettable liquid may
further contain a polymerization inhibitor to restrain polymerization by
heat or actinic radiation, at least one acid functionalized monomer or
oligomer, at least one elastomer, at least one surfactant for controlling
the spreading of the curable jettable liquid droplet, at least one
colorant for increasing the contrast between the jetted image and the
background. The curable jettable liquid may further contain water and/or
organic liquids, such as alcohols, fluorinated solvents and dipolar
aprotic liquids.

[0140]The curable jettable liquid may also further contain at least one
humectant, at least one biocide to prevent unwanted microbial growth over
time. In addition, the curable jettable liquid may further contain
additives such as buffering agents, anti-mold agents, pH adjustment
agents, electric conductivity adjustment agents, chelating agents,
anti-rusting agents and light stabilizers. Such additives may be
incorporated in the curable jettable liquid in any effective amount, as
desired. Examples of pH controlling agents suitable for curable jettable
liquid include, but are not limited to, acids, and bases, including
hydroxides of alkali metals such as lithium hydroxide, sodium hydroxide
and potassium hydroxide.

[0141]The curable jettable liquid preferably has a viscosity at a shear
rate of 100 s-1 and at a temperature between 15 and 70° C. of
not more than 100 mPas, preferably less than 50 mPas, and more preferably
less than 15 mPas.

Monofunctional Monomers

[0142]Any polymerizable monofunctional monomer commonly known in the art
may be employed. Particular preferred polymerizable monofunctional
monomers are disclosed in EP 1 637 926 paragraph [0054] to [0058]. Two or
more monofunctional monomers can be used in combination. The
monofunctional monomer preferably has a viscosity smaller than 30 mPas at
a shear rate of 100 s-1 and at a temperature between 15 and
70° C.

Polyfunctional Monomers and Oligomers

[0143]Any polymerizable polyfunctional monomer and oligomer commonly known
in the art may be employed. Particular preferred polyfunctional monomers
and oligomers are disclosed in EP 1 637 926 paragraph [0059] to [0063].

[0144]Two or more polyfunctional monomers and/or oligomers can be used in
combination.

[0145]The polyfunctional monomer or oligomer preferably has a viscosity
larger than 50 mPas at a shear rate of 100 s-1 and at a temperature
between 15 and 70° C.

Acid Functionalized Monomers and Oligomers

[0146]Any polymerizable acid functionalized monomer and oligomer commonly
known in the art may be employed. Particular preferred acid
functionalized monomers and oligomers are disclosed in EP 1 637 926
paragraph [0066] to [0070].

Photo-Initiators

[0147]The photo-initiator, upon absorption of actinic radiation,
preferably UV-radiation, forms free radicals or cations, i.e. high-energy
species inducing polymerization and crosslinking of the monomers and
oligomers in the jettable curable liquid.

[0148]A preferred amount of photo-initiator is 1 to 10% by weight, more
preferably 1 to 7% by weight, of the total curable jettable liquid
weight.

[0149]A combination of two or more photo-initiators may be used. A
photo-initiator system, including a photo-initiator and a co-initiator,
may also be used. A suitable photo-initiator system includes a
photo-initiator, which upon absorption of actinic radiation forms free
radicals by hydrogen abstraction or electron extraction from a second
compound, the co-initiator. The co-initiator becomes the actual
initiating free radical.

[0150]Irradiation with actinic radiation may be realized in two steps,
each step using actinic radiation having a different wavelength and/or
intensity. In such cases it is preferred to use 2 types of
photo-initiators, chosen in function of the different actinic radiation
used.

[0152]Suitable polymerization inhibitors include phenol type antioxidants,
hindered amine light stabilizers, phosphor type antioxidants,
hydroquinone monomethyl ether commonly used in (meth)acrylate monomers,
and hydroquinone, methylhydroquinone, t-butylcatechol, pyrogallol may
also be used. Of these, a phenol compound having a double bond in
molecules derived from acrylic acid is particularly preferred due to its
having a polymerization-restraining effect even when heated in a closed,
oxygen-free environment. Suitable inhibitors are, for example,
SUMILIZER® GA-80, SUMILIZER® GM and SUMILIZER® GS produced by
Sumitomo Chemical Co., Ltd.

[0153]Since excessive addition of these polymerization inhibitors will
lower the sensitivity to curing of the curable jettable liquid, it is
preferred that the amount capable of preventing polymerization be
determined prior to blending. The amount of a polymerization inhibitor is
generally between 200 and 20 000 ppm of the total curable jettable liquid
weight.

Oxygen Inhibition

[0154]Suitable combinations of compounds which decrease oxygen
polymerization inhibition with radical polymerization inhibitors are:
2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butane-1 and
1-hydroxy-cyclohexyl-phenyl-ketone; 1-hydroxy-cyclohexyl-phenyl-ketone
and benzophenone;
2-methyl-1[4-(methylthio)phenyl]-2-morpholino-propane-1-on and
diethylthioxanthone or isopropylthioxanthone; and benzophenone and
acrylate derivatives having a tertiary amino group, and addition of
tertiary amines. An amine compound is commonly employed to decrease an
oxygen polymerization inhibition or to increase sensitivity. However,
when an amine compound is used in combination with a high acid value
compound, the storage stability at high temperature tends to be
decreased. Therefore, specifically, the use of an amine compound with a
high acid value compound in ink-jet printing should be avoided.

[0155]Synergist additives may be used to improve the curing quality and to
diminish the influence of the oxygen inhibition. Such additives include,
but are not limited to ACTILANE® 800 and ACTILANE® 725 available
from AKZO NOBEL, EBECRYL® P115 and EBECRYL® 350 available from
UCB CHEMICALS and CD 1012, Craynor CN 386 (amine modified acrylate) and
Craynor CN 501 (amine modified ethoxylated trimethylolpropane
triacrylate) available from CRAY VALLEY.

[0156]The content of the synergist additive is in the range of 0 to 50% by
weight, preferably in the range of 5 to 35% by weight, based on the total
weight of the curable jettable liquid.

Plasticizers

[0157]Plasticizers are usually used to improve the plasticity or to reduce
the hardness of adhesives, sealing compounds and coating compositions.
Plasticizers are liquid or solid, generally inert organic substances of
low vapor pressure.

[0159]The amount of plasticizer is preferably at least 5% by weight, more
preferably at least 10% by weight, each based on the total weight of the
curable jettable liquid. The plasticizers may have molecular weights up
to 30 000 but are preferably liquids having molecular weights of less
than 5 000.

Elastomers

[0160]The elastomer may be a single binder or a mixture of various
binders. The elastomeric binder is an elastomeric copolymer of a
conjugated diene-type monomer and a polyene monomer having at least two
non-conjugated double bonds, or an elastomeric copolymer of a conjugated
diene-type monomer, a polyene monomer having at least two non-conjugated
double bonds and a vinyl monomer copolymerizable with these monomers.

[0162]The surfactant(s) may be anionic, cationic, non-ionic, or
zwitter-ionic and are usually added in a total quantity below 20% by
weight, more preferably in a total quantity below 10% by weight, each
based on the total curable jettable liquid weight.

[0163]A fluorinated or silicone compound may be used as a surfactant,
however, a potential drawback is bleed-out after image formation because
the surfactant does not cross-link. It is therefore preferred to use a
copolymerizable monomer having surface-active effects, for example,
silicone-modified acrylates, silicone modified methacrylates, fluorinated
acrylates, and fluorinated methacrylates.

Colorants

[0164]Colorants may be dyes or pigments or a combination thereof. Organic
and/or inorganic pigments may be used.

[0167]The pigment is present in the range of 0.01 to 10% by weight,
preferably in the range of 0.1 to 5% by weight, each based on the total
weight of curable jettable liquid.

Solvents

[0168]The curable jettable liquid preferably does not contain an
evaporable component, but sometimes, it can be advantageous to
incorporate an extremely small amount of a solvent to improve adhesion to
the ink-receiver surface after UV curing. In this case, the added solvent
may be any amount in the range of 0.1 to 10.0% by weight, preferably in
the range of 0.1 to 5.0% by weight, each based on the total weight of
curable jettable liquid.

Humectants

[0169]When a solvent is used in the curable jettable liquid, a humectant
may be added to prevent the clogging of the nozzle, due to its ability to
slow down the evaporation rate of curable jettable liquid.

[0170]Suitable humectants are disclosed in EP 1 637 926 paragraph [0105].
A humectant is preferably added to the curable jettable liquid
formulation in an amount of 0.01 to 20% by weight of the formulation,
more preferably in an amount of 0.1 to 10% by weight of the formulation.

Biocides

[0171]Suitable biocides include sodium dehydroacetate, 2-phenoxyethanol,
sodium benzoate, sodium pyridinethion-1-oxide, ethyl p-hydroxy-benzoate
and 1,2-benzisothiazolin-3-one and salts thereof. A preferred biocide for
the curable jettable liquid suitable for the method for manufacturing a
flexographic printing plate according to the present invention, is
PROXEL® GXL available from ZENECA COLOURS.

[0172]A biocide is preferably added in an amount of 0.001 to 3% by weight,
more preferably in an amount of 0.01 to 1.00% by weight, each based on
curable jettable liquid.

Preparation of a Curable Jettable Liquid

[0173]The curable jettable liquids may be prepared as known in the art by
mixing or dispersing the ingredients together, optionally followed by
milling, as described for example in EP 1 637 322 paragraph [0108] and
[0109].

EXAMPLES

Materials

[0174]All materials used in the following examples were readily available
from Aldrich Chemical Co. (Belgium) unless otherwise specified.
[0175]BR 7432 is an urethane acrylate oligomer from BOMAR SPECIALTIES
[0176]BR 7432 G is an urethane acrylate oligomer from BOMAR SPECIALTIES
[0177]SR 604 is a polypropyleneglycolmethacrylate from CRAY VALLEY
[0178]SR 506D is an isobornyl acrylate available from CRAY VALLEY
[0179]SR 531 is a cyclic trimethylolpopane formal acrylate from CRAY
VALLEY [0180]SR 285 is a tetrahydrofurfuryl acrylate from CRAY VALLEY
[0181]SR 340 is a 2-phenoxyethyl methacrylate from SARTOMER [0182]CN137
is a low viscosity acrylate oligomer from SARTOMER [0183]GENOMER 1122 is
a monofunctional urethane acrylate [0184]MIRAMER M100 is a dicaprolactone
acrylate from RAHN AG [0185]IRGACURE 651 is a photo-initiator from
CIBA-GEIGY [0186]IRGACURE 500 is a photo-initiator from CIBA-GEIGY
[0187]IRGACURE 127 is a photo-initiator from CIBA-GEIGY [0188]IRGACURE
819 is a photo-initiator from CIBA-GEIGY [0189]EBECRYL 11 is a
polyethylene glycol diacrylate available from UCB [0190]EBECRYL 168 is an
acid modified methacrylate available from UCB [0191]EBECRYL 770 is an
acid functional polyester acrylate diluted with 40% HEMA available from
UCB [0192]EBECRYL 1039 is a urethane monoacrylate from UCB [0193]EBECRYL
1360 is a polysiloxane hexaacrylate from UCB [0194]VERBATIM LDR32, a
liquid photopolymer from Chemence [0195]VERBATIM ACCLAIM 25, a liquid
photopolymer from Chemence [0196]VERBATIM ACCLAIM 32, a liquid
photopolymer from Chemence [0197]VERBATIM LF 25C, a liquid photopolymer
from Chemence [0198]VERBATIM LF 32C, a liquid photopolymer from Chemence
[0199]VERBATIM 180 SP Clear, a liquid photopolymer from Chemence
[0200]VERBATIM LF 25C, a liquid photopolymer from Chemence [0201]VERBATIM
HR50, a liquid photopolymer from Chemence [0202]BHT is
2,6-di-t-buthyl-4-methylphenol from ALDRICH [0203]MH is 5 wt % of
2-methyl-hydrochinon from MITSUI in DPGDA [0204]Santicizer 278 is
available from MONSANTO [0205]Perenol S Konz is a polysiloxane from
HENKEL [0206]Yellow dye is
2-(4-{Butyl-[4-(2-methoxy-ethoxy)-phenyl]-amino}-benzylidene)-malononitri-
le available from AGFA [0207]Magenta dye is
2-Cyano-3-(4-dibutylamino-phenyl)-but-2-enedinitrile available from AGFA.

Example 1

Preparation of the Curable Inkjet Fluid IF-01

[0208]Inkjet fluid IF-01 was prepared by mixing the ingredients listed in
Table 1.

[0210]The photosensitive layers PL-01 to PL-06 were coated on a subbed
polyester at a thickness of 290 μm. The subbing layer on the polyester
had the following composition: 79.10 wt % of a copolymer
vinylidenechloride-methylacrylate-itaconic acid (88/10/2); 18.60 wt %
Kieselsol 100F from Bayer; 0.40 wt % Mersolat H from Bayer; 1.90 wt %
Ultravon W from Ciba-Geigy.

Curing of the Coated Photosensitive Layers PL-01 to PL-06

[0211]UV-curing was performed on the coated layers PL-01 to PL-06 by 10
passages through a DRSE-120 conveyer, from FUSION UV SYSTEMS Ltd.
equipped with a D-bulb. The conveyer speed was 20 m/min.; a power setting
of 100% was used (=0.9 J/cm2 on the surface of the coated layers).

Applying the Inkjet Fluid IF-01 on the Cured Layers PL-01 to PL-06

[0212]The inkjet fluid IF-01 was applied to the cured layers PL-01 to
PL-06 with a paint brush system. The droplets were cured by passing the
samples 8 times through the DRSE-120 conveyer described above. An UV-C
postcuring was carried out with a light box equipped with 4 Philips TUV
lamps (λmax=254 nm) during 20 minutes.

Adhesion

[0213]The adhesion of the cured inkjet droplets on the cured layers PL-01
to PL-06 was evaluated as follows:

[0214]An ASTM tape from Peramcel was provided on both sides of the
flexographic printing forme, i.e. one ASTM tape in contact with the cured
droplets, the other ASTM tape on the backside of the PET support. After
separating the ASTM tapes, it was found that the cured droplets were not
detached from the cured layers PL-01 to PL-06.

Example 2

Preparation of the Photosensitive Layer PL-07

[0215]The coating solution of the photosensitive layer PL-07 was prepared
by mixing the ingredients listed in Table 3.

[0216]The photosensitive layer PL-07 was coated on a subbed polyester (see
example 1) at a thickness of 290 μm.

Curing of the Coated Photosensitive Layer PL-07

[0217]UV-curing was performed on the coated layer PL-07 by 10 passages
through the DRSE-120 conveyer described above.

Applying the Inkjet Fluid IF-01 on the Cured Layer PL-07

[0218]The inkjet fluid IF-01 was applied with a paint brush system on the
cured layer PL-07 with a paint brush system. The droplets were cured by
passing the samples 8 times through the DRSE-120 conveyer described
above. An UV-C postcuring was carried out with a light box equipped with
4 Philips TUV lamps (λmax=254 nm) during 20 minutes.

Adhesion

[0219]The adhesion of the cured inkjet droplets on the differently cured
photolayer PL-07 was evaluated as described in Example 1.

[0220]After separating the ASTM tapes, it was found that the cured
droplets were not detached from the cured layer PL-07.

Example 3

Preparation of the Curable Inkjet Fluid IF-02

[0221]Inkjet fluid IF-02 was prepared by mixing the ingredients listed in
Table 4.

[0223]The formulation of Table 5 was coated on a subbed polyester support
(see example 1) at a thickness of 290 μm.

Curing of the Coated Photosensitive Layer PL-08

[0224]The coated photosensitive layer PL-08 was put in a nitrogen box. The
oxygen was removed while circulating nitrogen. UV-A curing was carried
out with a UV-A light box equipped with 8 Philips TL 20 W/10
(λmax=370 nm) during 30 seconds. The distance between the
sample and the curing lamps was approximately 10 cm.

Applying the Inkjet Fluid IF-02 on the Cured Layer PL-08

[0225]The inkjet fluid IF-02 was applied with a paint brush on the cured
photosensitive layer PL-08. UV-A curing was carried out in a UV-A light
box equipped with 8 Philips TL 20 W/10 (λmax=370 nm) under
nitrogen during 3 minutes. The distance between the sample and the curing
lamps was approximately 10 cm. An UV-C postcuring was carried out with a
light box equipped with 4 Philips TUV lamps (λmax=254 nm)
during 20 minutes.

Adhesion

[0226]The adhesion of the cured fluid IF-02 droplets on the photolayer
PL-08 was evaluated as described in Example 1.

[0227]After separating the ASTM tapes, it was found that the cured
droplets were not detached from the cured layer PL-08.

Example 4

Preparation of the Curable Inkjet Fluid IF-03

[0228]Inkjet fluid IF-03 was prepared by mixing the ingredients listed in
Table 6.

[0230]The formulation of Table 7 was coated on a subbed polyester support
(see example 1) at a thickness of 290 μm.

Curing of the Coated Photosensitive Layer PL-09

[0231]One sample of the coated PL-09, PL-0/01, was UV-A cured in a UV-A
light box during 2 minutes (λmax=370 nm), followed by an UV-C
curing during 20 minutes in a UV-C light box (λmax=254 nm).
Sample PL-09/01 did not show any tackiness, indicating that it is
completely cured.

[0232]Another sample of the coated PL-09, PL-09/02, was UV-A cured in a
UV-A light box during 9 seconds. Sample PL-09/02, after curing, did show
some tackiness, indicating that it is not completely cured, i.e.
partially cured.

Applying the Inkjet Fluid if-03 on the Samples PL-09/01 and /02.

[0233]The inkjet fluid IF-03 was applied with a paint brush system on the
samples PL-09/01 and /02. UV-A curing was carried out in an UV-A light
box equipped with 8 Philips TL 20 W/10 (λmax=370 nm) under
nitrogen during 2 minutes. The distance between the sample and the curing
lamps was approximately 10 cm. An UV-C postcuring was carried out with a
light box equipped with 4 Philips TUV lamps (λmax=254 nm)
during 20 minutes.

Adhesion

[0234]The adhesion of the droplets of IF-03 on both samples PL-09/01 and
/02 was determined using a manual peel test. With a sharp knife, the
detachability of the droplets was investigated.

[0235]The droplets of IF-03, jetted on the completely cured sample
PL-09/01 could be detached rather easily. In contrast, it was impossible
to detach the droplets of IF-03, jetted on the partially cured sample
PL-09/02.

[0236]This example indicates very clearly that adhesion of the relief
image, formed by image wise jetting of curable fluids on a partially
cured "floor" is stronger compared to the adhesion of the relief image on
a completely cured "floor". An explanation may be the presence of
unreacted monomer in "floor" upon partial curing, which may react with
monomers of the relief image upon overall curing.

[0237]While preferred embodiments of the present invention have been
described above, it is to be understood that variations and modifications
will be apparent to those skilled in the art without departing the scope
and spirit of the present invention. The scope of the present invention,
therefore, is to be determined solely by the following claims.